Lowrance Help

Hey all. I have a Lowrance x85 with a shoot-thru hull mounted transducer.
It has worked perfectly for almost two years, but now - if you are familiar
with it - the digital sonar and auto functions do not work. It will not
give you a digital readout of depth, it just flashes. However when in
"fast-track mode" and I manuall range the depth, it works. So, I sent it
in, it came back and the factory said it was fine.

Knowing that the record bass was slipping away from me, I borrowed a buds
spare transom unit, hooked it up and the unit works fine? I switched the
thru-hull transducer to the one my highspeed depth finder uses, and viola,
it worked - for two weeks then behaves as above.

Questions:
Has anyone had sonar units break thru-hull transducers? Seen anything like
this before? I've tried isolating electrical interference, etc. But I'm
talking sitting in the middle of the lake, nothing on - blowers, live well,
etc.

Thanks,
-J